1. Field of the Invention
The present invention relates to an ultrasonic probe to be inserted into a narrow portion such as a hole, a hollow or the like, and particularly inserted into a blood vessel of a heart for carrying out a mechanical radial or sector scanning within the blood vessel.
2. Description of the Background Art
In FIG. 1, there is shown a conventional ultrasonic probe 1 of a mechanical radial scanning type. In the probe 1, an oscillator 2 having a diameter of approximately 2 mm is arranged in a tip of a tubular case 5, and a mirror 3 is arranged in opposition to the oscillator 2 within the tubular case 5 and is surrounded by a ultrasonic wave propagation material 8 such as water or a physiological saline solution. The mirror 3 is secured to a shaft 3a which is connected to a rotary transmission shaft 4 having an outer diameter of approximately several mm, which is composed of a tubular coil or coil spring 4a made of a steel wire. In the tubular case 5, the shaft 3a of the mirror 3 is supported by a bearing 6 mounted on the case 5 through the rotary transmission shaft 4. The rotary transmission shaft 4 is connected to a driver such as a motor M or the like. When the motor M is driven, a rotary driving force in an X-direction is transmitted to the mirror 3 through the rotary transmission shaft 4 to rotate the mirror 3 in a Y-direction, and the mirror reflects a ultrasonic wave radiated by the oscillator 2 to carry out a ultrasonic wave scanning in a radial plane F.
In FIG. 2, there is shown another conventional ultrasonic probe 10 of a mechanical radial scanning type. In the probe 10, an oscillator 12 having a diameter of approximately 2 mm is arranged in a tip of a tubular case 15, and a mirror 13 is arranged in opposition to the oscillator 12 within the tubular case 15. The mirror 13 is secured to a shaft 13b having a hollow 13a in its end, and a rotary transmission shaft 14 composed of a steel wire having a diameter of approximately 1 mm is connected to the shaft 13b by inserting one end of the rotary transmission shaft 14 in the hollow 13a of the shaft 13b. In the tubular case 15, the shaft 13b of the mirror 3 is supported by a bearing 16 mounted on the case 15. The rotary transmission shaft 14 is connected to the motor M to function in the same manner as the rotary transmission shaft 4 shown in FIG. 1.
When the above described probe 1 or 10 is inserted into blood vessels such as aorta B.sub.1 having a diameter of approximately 20 to 30 mm, coronary artery (chief trunk portion) B.sub.2 having a diameter of approximately 3 to 5 mm and ramus circumflexus B.sub.3 having a diameter of less than 2 mm or ramus descendens B.sub.4 having a diameter of less than 2 mm of a heart H of an adult, as shown in FIG. 3, in order to carry out a ultrasonic wave scanning in a radial plane F or the internal surfaces of the blood vessels, the probe 1 or 10 is first inserted from its oscillator 2 or 12 into the aorta B.sub.1, and is then bent at an angle of approximately 90 degree to go into the coronary artery B.sub.2. Then, the oscillator 2 or 12 of the probe 1 or 10 is bent in an inclined direction to be inserted into the fine ramus circumflexus B.sub.3 or ramus descendens B.sub.4. Then, by driving the motor M, the mirror 3 or 13 is rotated to perform a mechanical radial scanning in the ramus circumflexus B.sub.3 or ramus descendens B.sub.4. A ultrasonic probe capable of clinically performing a ultrasonic wave scanning in a radial plane within a fine blood vessel such as the ramus circumflexus B.sub.3 or ramus descendens B.sub.4 has been demanded.
However, in one conventional ultrasonic probe 1 shown in FIG. 1, since, even when an oscillator 2 having a diameter of less than 2 mm is used, the diameter of the rotary transmission shaft 4 is big such as several mm over its entire length, it is impossible to insert the probe 1 into a fine blood vessel such as the ramus circumflexus or ramus descendens.
Further, in another conventional ultrasonic probe 10 shown in FIG. 2, since the rotary transmission shaft 14 is composed of a linear steel wire, when the transmission shaft 14 is largely bent, one side having a small curvature of the transmission shaft 14 receives a compression force and another side having a large curvature receives an extension force. Accordingly, even when the motor M is rotated 90 degree, the mirror 13 connected to the transmission shaft 14 often rotates only 30 degrees due to such a stress given to the transmission shaft 14, that is, the rotating force of the motor M can not be smoothly transmitted to the mirror 13. Hence, an uneven or irregular rotation of the mirror 13 is caused, and a good ultrasonic wave image can not be obtained.